How Much Coolant in Oil in Order to Be Visible?
 

Strange question, I know....just looking for a little hand holding while I wait to do an oil analysis. I'd say I've lost a solid inch, perhaps more, of coolant (measuring expansion tank level)....but have not observed any leaks. Oil in the dipstick is jet black...I may extract a quart or so this afternoon to see what I see.

Oil's been in there 7500 miles. If I pull some out, and see no milkiness whatsoever, can I safely assume that that coolant has not gone into the engine?

You might consider just a simple blot test on a napkin.

Head gasket can be an issue on your 602's. I believe it should be milky? Plenty of places for coolant to go, especially in the winter (heater core).

Part of my thinking is that, if I can rule out coolant in the engine, then I can relax a little bit...no real rush to get it diagnosed.

Please excuse my ignorance....how much oil would I use and what would I be looking for?

two separate dipstick drops on a clean white paper towel would be sufficient.

compare the 'spread' of the oil from your engine with the 'spread' from new oil. The spread should be similar. It the oil has water, it should be pretty evident.

keep in mind that the temperature of the oil should be the same so leave the new oil container outside overnight.

not scientific but more ballpark. sufficient for your purpose I think.

Better still, I have a "control car"....I can compare oil from my 91 300D to oil from my 92 300D.

Such a test will yield nothing as you don't have any water in your oil.........it has boiled away long ago.

What remains is glycol and some sodium that will be evident on an oil analysis.

I wouldn't waste my time on any test that can yield no definitive results.

If you have water getting into your oil, one would expect to find whipped cream on the inside of your valve cover. Lift the cap, run your finger around the inside & if all you have is black oil, chances are the coolant is not going there.
Did you consider that you could have had a post shutdown boil from heat soak ? The water could have been boiled out. It boils in the head & sort of does a reverse burp, a bit like gastric reflux.

Blackstone Labs
 

Send a sample to Blackstone laboratory. They can determine if there is coolant in the oil by measuring the level of sodium in the oil. Costs $25 for the analysis. http://blackstone-labs.com/

If you call or email them they will send you a free sampling kit with the packaging necessary to mail it to them.

I'm doing it through AVlube (now Petroliance). So I'll know for certain soon enough.

Yes, I'd thought about that. So, what, just replace the expansion tank cap?

I'm also thinking it could be the overflow system.

At this point my goal is to rule out the engine....then I can relax a bit.

like Brian Carlton says... if you've been driving your engine, the water is long gone. unless you are dumping a garden hose into the oilpan, you're not going tofind milk.
oil analysis is the only way to be sure.

So let me ask this: if a leak of coolant into the engine is slow enough that all the water is constantly burned off, how is the engine harmed? Or is it?

Depending on the size of the leak and how frequent the oil changes, the glycol accumulation in the oil can potentially harm the bearings.

However, I do believe that this phenomenon is a bit overrated and the leak would have to be significant for this to occur.